A steered axle assembly normally has a relatively fixed axle member or beam on which a pair of wheel supports are pivotal about respective upright wheel pivot or king-pin axes spaced horizontally apart on the beam generally perpendicular to a predetermined horizontal travel direction. A track rod extends horizontally transverse, that is generally perpendicular, to the travel direction between the wheel supports and has outer ends pivoted on same about respective upright track axes spaced in the travel direction from the respective pivot axes. An actuator, either a steering box or a hydraulic or pneumatic booster, has an output element connected to the track rod between the track axes for displacing the rod horizontally generally perpendicular to the travel direction and thereby generally identically pivoting the wheel supports about the respective wheel pivot axes.
As originally manufactured this equipment invariably allows the wheel supports to pivot through a much greater arc than is in practice permissible. The extent of pivot of the wheel supports is limited to prevent the tires from coming into contact with the adjacent structure of the vehicle, for instance the inside of the wheel well or the fender.
Thus the standard system simply provides respective abutments or bumps formed on the axle beam adjacent the wheel supports and facing generally tangentially of the respective wheel pivot axes. These supports in turn are each formed with a tangentially extending threaded bore receiving an adjustment bolt having a head engageable with a respective abutment in a respective end position of the wheel supports. The bolts can be screwed out from the wheel supports to decrease the turning arc in the respective direction, or screwed in to increase it. Lock nuts are provided to secure the bolts in the set positions.
Setting or changing the adjustment in such an arrangement is quite difficult. Assuming the pivot arc is to be reduced, the wheels are cramped all the way in one direction to the desired end point, and then the one bolt is screwed out until it touches its abutments, whereupon it is locked in place. The wheels are then oppositely pivoted and the operation is performed at the other end of the axle. This operation must be carried out whenever tire or wheel size is changed, as is common on large pieces of equipment. If it is not done valuable tires and the vehicle both can be damaged, particularly in systems wherein a heavy-duty actuator provides all of or boosts the steering force.
The adjustment bolts are quite inaccessible, especially when the respective wheel is in a cramped-over end position. In addition adjustment is continuous, so that each adjustment must be painstakingly executed to assure uniform results. The adjustment mechanism itself is in a location where it is subject to much fouling, so the bolts frequently become badly frozen in place. The transversely effective vector of force on the bolts can bend them, and it is also simply possible for them to vibrate loose and become maladjusted.